Regarding syphilis, all are true, except -a) VDRL titre decreases or even absent after treatmentb) VDRL becomes positive after 10-14 days of infectionc) Earliest serological test to become positive in untreated primary syphilis is TPHAd) Yaws and Pinta cannot be differentiated

**Core Concept**
Syphilis is a chronic bacterial infection caused by Treponema pallidum, transmitted primarily through sexual contact. The diagnosis of syphilis is made through serological tests, which detect the presence of antibodies against the bacterium.

**Why the Correct Answer is Right**
The VDRL (Venereal Disease Research Laboratory) test is a non-treponemal test that detects the presence of antibodies against the lipoidal material released from damaged host cells and the bacteria. After successful treatment, the VDRL titre decreases or becomes absent as the body clears the antibodies. On the other hand, treponemal tests such as TPHA (Treponema pallidum hemagglutination assay) become positive within 2-3 weeks of infection and remain positive for life, even after treatment. In contrast, non-treponemal tests like VDRL become positive after 10-14 days of infection.

**Why Each Wrong Option is Incorrect**
* **Option B:** This statement is incorrect because VDRL becomes positive after 10-14 days of infection, not immediately.
* **Option C:** This statement is incorrect because the RPR (Rapid Plasma Reagin) test is the earliest non-treponemal test to become positive in untreated primary syphilis, not TPHA.
* **Option D:** This statement is incorrect because Yaws can be differentiated from Pinta through serological tests. Yaws is caused by Treponema pallidum subspecies pertenue and typically presents with skin lesions and a positive VDRL test, whereas Pinta is caused by Treponema carateum and presents with skin lesions and a negative VDRL test.

**Clinical Pearl / High-Yield Fact**
It is essential to note that a negative VDRL test does not rule out syphilis, especially in the early stages of the disease. A negative test result may be due to the window period or the presence of a treponemal test that is not yet positive.

**Correct Answer: A**